The present invention relates to a method to measure the volumetric flow in blood vessels using a pulsed Doppler instrument. The invention relates to an invasive method by using of a commercially available Doppler flow wire system which allows simultaneously assessment of crossectional area and mean velocity, thus providing real volumetric flow. The invention further relates to an non-invasive method to measure volumetric flow in the heart and in large vessels.
Volumetric blood flow is formally defined as product of mean flow velocity and corresponding vessel cross-sectional area. Accordingly, volumetric coronary blood flow can be measured by simultaneously assessing vessel size (using either quantitative angiography or intravascular ultrasound) and blood flow velocity (using intravascular Doppler). Very often, however, vessel size is not assessed and measurement of volumentric coronary blood flow relies on blood flow velocity alone, assuming that the vessel diameter remains constant during different flow conditions. Since in the assessment of coronary flow reserve (CFR; ratio of hyperemic over resting flow) it is a standard procedure to pharmacologically induce coronary hyperemia, which by definition changes coronary vessel size, this assumption is wrong. In addition, commercially available Doppler flow wire systems allow assessment of average peak velocity (APV) but not mean velocity. For the calculation of mean flow velocity from the APV a constant coefficient of 0.5 is commonly used. Unfortunately, this is only correct for Newtonian fluids but not for blood where this coefficient is very variable. Thus, the use of APV to assess CFR suffers from fundamental limitations and may produce misleading results, as it is not based on real volumetric blood flow measurement.
In 1979, Hottinger and Meindl described a noninvasive method to measure volumetric flow using a dual beam pulsed Doppler instrument. One sample volume intersects completely the vessel cross-section, whereas the other lays entirely within the vessel lumen. Combining the results of these two measurements, compensation for the effects of attenuation and scattering is achieved, and volumetric flow is obtained from the Doppler signal power. This method, which is independent of velocity profile, vessel geometry and Doppler angle, was later applied to an intravascular Doppler ultrasound catheter designed for intravascular measurement of volumetric blood flow. Recently, accurate volumetric flow measurements in small tubes and even in coronary arteries have been reported using power-ratio or decorrelation of radiofrequency ultrasound signals.
However, these methods are either time-consuming or they require special devices of large size (2.9 or 3.2 French), unsuitable for use in distal coronary arteries. We present the in vitro validation of a newly developed invasive method for calculation of volumetric coronary blood flow, based on the attenuation-compensated Hottinger-Meindl method. The novelty of this method is the use of a commercially available Doppler flow wire system which allows simultaneously assessment of cross-sectional area and mean velocity, thus providing real volumetric flow. We further present a method to measure volumetric flow in large vessels.